SS - Energies of ionic solids

Question 1

Define lattice energy

Answer 1

The lattice energy is the energy change when one mole of gaseous ions, which are infinitely separated, form a crystal at 0K.

Question 2

Describe how to calculate lattice energies

Answer 2

We assume that the crystal is purely ionic, and electrostatic interactions described by Coulomb forces hold the crystal together.

Question 3

Describe two factors that determine r₀

Answer 3

Question 4

Give and describe the equation for the energy change upon bringing two ions from infinite separation to a separation of r

Answer 4

Question 5

Give and describe the equation for the energy change upon bringing two ions from infinite separation to a separation of r using Madelung constants

Answer 5

Question 6

Define a madelung constant

Answer 6

Madelung constants are structure-specific and are calculated by adding the charge x 1/distance relative to r.

Question 7

Give the model for the repulsive component of r₀

Answer 7

n = Born exponent

B = repulsive constant

r is the separation between the species of interest

Question 8

Give the full equation for lattice energy (ie by combining the repulsive part with the attractive part)

Answer 8

Question 9

Describe how to find the minimum potential energy

Answer 9

Differentiate and solve dU/dr = 0 for B. Substituting B into the original equation for U gives the Born-Landé equation

Question 10

Describe Hess’ law

Answer 10

The enthalpy difference between two states A and B is independent of the route taken

Question 11

Give and describe the Kapustinskii equation

Answer 11